Method for producing plate-, tape- or film-shaped Si crystal bodies for solar cells

Abstract

Large surfaced, pore-free silicon bodies useful for processing into solar cells are produced by providing at least two layers formed from at least two distinct silicon materials, each containing different amounts of germanium therein and thus having different melting points. A laminate is formed of such layers and sintered at a temperature at which only one of the silicon materials becomes molten so that the resultant molten layer effectively seals the pores of the other layers and upon cooling a unitary silicon body is attained. In certan embodiments, a molten silicon material is applied as a liquified film onto a solidified layer composed of different silicon material.

I claim as my invention: 
     
       1. In a method of producing plate-, tape- or film-shaped Si crystal bodies having crystalline pillar structures therein, which are essentially equivalent to crystalline columnar structures, without melting of the base material which forms such Si bodies and which bodies are useful for further processing into large-surface solar cells, which includes the steps of: (a) forming a slurry from an admixture of a Si powder having an average particle size in the range of less than about 1 μm, optional additives and a compatible liquid binder;   (b) extruding such layer with an extrusion means onto a first inert support member as a relatively thin slurry layer, which is dried into a self-supporting layer and removing the support member; and   (c) sintering the self-supporting layer on a temperature-stable second inert support member in a protective gas atmosphere at a sintering temperature ranging from about 1350° C. to below about 1430° C. in such a manner that a layer of Si crystal particles is generated, each particle having an average particle diameter substantially corresponding to the thickness of the self-supporting layer; the improvement comprising:     forming at least two layers in accordance with steps (a) and (b) from different silicon materials, with a first layer being formed from a first silicon material having the formula (Si+xGe) wherein x is a numeral ranging from 0 to 5 gram atomic percent and a second layer being formed from a second silicon material having the formula [Si+(x+y)Ge] wherein x is a numeral ranging from 0 to 5 gram atomic percent and y is a numeral greater than 0 and ranging up to 5 gram atomic percent, with the proviso that y has such a value that said second material has a melting point enough below that of said first sintering material;   positioning said layers onto one another and subjecting the resultant stack to sintering in accordance with step (c) at a temperature at which only said second silicon material becomes molten; and   cooling the sintered structure to obtain a unitary Si body.   
     
     
       2. In a method as defined in claim 1 wherein y is about 1 gram atomic percent. 
     
     
       3. In a method of producing plate-, tape- or film-shaped Si crystal bodies having crystalline pillar structures therein, which are essentially equivalent to crystalline columnar structures, without melting of the base material which forms such Si bodies and which bodies are useful for further procesing into large-surface solar cells, which includes the steps of: (a) forming a slurry from an admixture of a Si powder having an average particle size in the range of less than about 1 μm, optional additives and a compatible liquid binder;   (b) extruding such layer with an extrusion means onto a first inert support member as a relatively thin slurry layer, which is dried into a self-supporting layer and removing the support member; and   (c) sintering the self-supporting layer on a temperature-stable second inert suport member in a protective gas atmosphere at a sintering temperature ranging from about 1350° C. to below about 1430° C. in such a manner that a layer of Si crystal particles is generated, each particle having an average particle diameter substantially corresponding to the thickness of the self-supporting layer; the improvement comprising:     applying a substantially uniform liquified film of a molten silicon material onto an entire surface of a solidified layer, said molten silicon material having the formula [Si+(x+y) Ge] wherein x is numeral ranging from 0 to 5 gram atomic percent and y is a numeral greater than 0 and ranging up to 5 gram atomic percent, said solidified material being composed of a silicon material having the formula (Si+xGe) wherein x is a numeral ranging from 0 to 5 gram atomic percent, said solidified layer being produced at least in accordance with steps (a) and (b); and   cooling the resultant structure to attain a unified Si body.   
     
     
       4. In a method as defined in claim 3 wherein said solidified layer is sintered in accordance with step (c) prior to application of said liquified film. 
     
     
       5. In a method as defined in claim 4 wherein during application of said liquified film, said solidified layer is cooled. 
     
     
       6. In a method as defined in claim 3, wherein said application of said liquified film occurs during sintering of said solidified layer. 
     
     
       7. In a method as defined in claim 3 wherein said solidified layer has a thickness in the range of about 100 to 200 μm. 
     
     
       8. In a method as defined in claim 7 wherein said liquified film is applied in a thickness less than about 100 μm. 
     
     
       9. In a method as defined in claim 3, wherein said liquified film is applied in a continuous manner on said solidified layer.